1. Field of the Invention
The present invention relates to an improved process or method for applying a coated or uncoated film onto at least one main surface of a lens substrate which can be implemented in a short period of time without any risk of deformation of the lens substrate and which allows a localized and controlled heating during implementation of the process.
The invention also relates to a coated film and a system for implementing the substrate coating process.
2. Description of Related Art
It is a common practice in the art to coat at least one main surface of a lens substrate, such as an ophthalmic lens or lens blank, with several coatings for imparting to the finished lens additional or improved optical and/or mechanical properties.
Thus, it is usual practice to coat at least one main surface of a lens substrate, typically made of an organic glass material, with successively, starting from the surface of the lens substrate, an impact-resistant coating (impact resistant primer), an abrasion and/or scratch-resistant coating (hard coat), an anti-reflecting coating and, optionally, a hydrophobic top coat. Other coatings such as a polarized coating, a photochromic or a dying coating may also be applied onto one or both surfaces of the lens substrate.
Numerous processes and methods have been proposed for coating a surface of an ophthalmic lens and are disclosed.
U.S. Pat. No. 6,562,466 describes one process or method for transferring a coating from at least one mold part onto at least a geometrically defined surface of a lens blank comprising:                providing a lens blank having at least one geometrically defined surface;        providing a support or mold part having an internal surface bearing a coating and an external surface;        depositing on said geometrically defined surface of said lens blank or on said coating a pre-measured amount of a curable adhesive composition;        moving relatively to each other the lens blank and the support to either bring the coating into contact with curable adhesive composition or bring the curable adhesive composition into contact with the geometrically defined surface of the lens blank;        applying a sufficient pressure onto the external surface of the support so that the thickness of a final cured adhesive layer is less than 100 micrometers;        curing the layer of adhesive composition; and        withdrawing the support or mold part to recover the lens blank with the coating adhered onto the geometrically defined surface of said lens blank.        
In the process of U.S. Pat. No. 6,562,466, a light or thermal curing adhesive is used to transfer the coating layers from the support to the surface of the lens substrate. The adhesive is required to stick both to the exposed film on the support and the surface of the lens substrate.
U.S. patent application Ser. No. 11/048,136 filed on Feb. 1, 2005 in the name of ESSILOR INTERNATIONAL (COMPAGNIE GENERALE D'OPTIQUE), hereby incorporated by reference, discloses a process for applying a coated or uncoated film onto at least one main surface of a lens substrate which comprises the steps of:                (a) providing a lens substrate having main surfaces;        (b) providing a coated or uncoated film;        (c) forming, on either face of the coated or uncoated film or one of the said main surfaces of the lens substrate, a layer of a dry latex;        (d) depositing at least one drop of a water base activating liquid on either one of the said main surfaces of the lens substrate, a face of the coated or uncoated film or an exposed surface of the dry latex layer;        (e) moving relatively to each other the coated or uncoated film and the lens substrate and applying a sufficient force to the coated or uncoated film to spread the water base activating liquid and form a thin pellicle of the water base activating liquid between the dry latex layer and either the lens substrate or the coated or uncoated film;        (f) heating the thin pellicle of water base activating liquid and the dry latex layer;        (g) releasing the applied force; and        (h) recovering the lens substrate with the coated or uncoated film adhered to the lens substrate main surface.        
Preferably, heating step (f) is performed at a temperature higher than the “tacky” temperature of the dry latex layer. The “tacky” temperature is the temperature at which the dry latex layer becomes sticky.
Typically, heating step (f) is performed at a temperature ranging from 40° C. to 130° C., preferably 50° C. to 120° C.
In U.S. patent application Ser. No. 11/048,136 heating source can be an air oven, a hot water bath, an IR source or a microwave source. However, this document does not give any information about microwave heating and how one could obtain a controlled heating essentially localized only in the area of the coated or uncoated film and the lens substrate, in particular when using an inflatable membrane apparatus for implementing the process.
Inflatable membrane apparatuses for implementation of coating application are disclosed in particular in published International Patent Application WO 03/004255 and in U.S. patent application Ser. No. 11/203,870 filed on 15 Aug. 2005 in the name of ESSILOR INTERNATIONAL (COMPAGNIE GENERALE D'OPTIQUE), both incorporated by reference.
The heating step is in fact commonly performed by placing the entire system including the pressing apparatus, the film, the heat activable adhesive layer and the lens substrate into a conventional convection oven and heating lasts about 30 minutes at a temperature typically set at about 110° C.
These heating procedures have the drawbacks of being energy consuming, because the entire system is heated, and necessitates long heating time to complete the process, for example about 30 minutes when using a dry latex layer and a water base activating liquid as the heat activable adhesive layer
Infrared heating has also been attempted. When using an inflatable membrane apparatus, if the infrared emitter is external to the accumulator, the IR radiation must pass through a quartz window and the membrane before impinging the film and the lens substrate which results in significant absorption of the IR radiation and inefficient heating leading to a poor film or coating adhesion. If the IR emitter is located within the accumulator, there is a high risk that the IR radiation will be too strong, resulting in a quick cracking and crazing of the coating. Furthermore, deflation of the membrane, especially when pressure is rapidly released, will likely damage or destroy the IR emitter.